Heteroaromatic hydrogen exchange reactions. Part VII. Isotope effects for the base-catalysed exchange of 3-2H1- and 3-3H1-indoles in aqueous sodium hydroxide

Abstract

Rates of protodedeuteriation in aqueous NaOH at 25 °C are reported for indole and 2-methylindole labelled at the 3-position, together with rates of deuteriodetritiation of the 2-methyl compound in NaOD. Calculation of various isotopic rate ratios from this and previous data for the corresponding protodetritiation reaction show unequivocally the incidence of an S_E2 mechanism involving the indole anion and water. Critical examination shows that the isotope effects for these reactions are relatively insensitive to the symmetry of the transition state for the protontransfer process.